L-grade stimulation fluid

ABSTRACT

A method of treating a subsurface formation comprises mixing an unfractionated hydrocarbon mixture, water, and natural gas with a foaming agent to form a stimulation fluid comprising foam. The unfractionated hydrocarbon mixture comprises ethane, propane, butane, isobutane, and pentane plus. The method further includes increasing a pressure of the stimulation fluid and injecting the stimulation fluid into the subsurface formation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application Ser. No. 62/311,793, filed Mar. 22, 2016, the contents of which are herein incorporated by reference in their entirety.

BACKGROUND

Field

Embodiments of the disclosure relate to methods and systems for providing stimulation fluids to treat (such as fracture) a subsurface formation (such as a hydrocarbon bearing reservoir). In particular, embodiments of the disclosure relate to providing hydraulic fracturing fluids configured to fracture hydrocarbon bearing reservoirs.

Description of the Related Art

Fracture treatments are utilized to improve fluid conductivity between a wellbore and a formation of interest to increase fluid production rate and associated reserves. Hydraulic fracture treatments are typically used in low-permeability formations, in conventional reservoirs to bypass near-wellbore permeability damage, and in unconventional reservoirs to intersect induced fractures with a natural fracture network.

A typical fracture treatment injects a viscous fluid into a formation of interest to open a fracture of a desired geometry. The viscous fluid carries a proppant into the opened fracture to maintain conductivity in the fracture after the fracture treatment is completed. Viscous fluids may have features that damage the permeability of the proppant pack and/or the formation near the fracture. For example, water-based fluids may imbibe into the formation face and reduce permeability, may precipitate scale, and may cause fines migration during well flow back and clean-up.

Recent data suggests that approximately 98% of the hydraulic fracture treatments in the U.S. utilize water-based technology. Water-based technology brings with it a host of water-based chemicals including acids, biocides, and corrosion inhibitors that expand the environmental footprint and cost associated with the fracture treatment. Water-based hydraulic fracture treatments also consume groundwater and aquifers in drought-prone regions such as Texas and Oklahoma. Very large volumes of water, often millions of gallons, are used to conduct a hydraulic fracture treatment to stimulate a single well.

Thus, there is a need for new and improved stimulation fluids for treating subsurface formations.

SUMMARY

In one embodiment, a method of treating a subsurface formation comprises mixing an unfractionated hydrocarbon mixture, water, and natural gas with a foaming agent to form a stimulation fluid comprising foam. The unfractionated hydrocarbon mixture comprises ethane, propane, butane, isobutane, and pentane plus. The method further includes increasing a pressure of the stimulation fluid and injecting the stimulation fluid into the subsurface formation.

In one embodiment, a method of treating a subsurface formation comprises mixing an unfractionated hydrocarbon mixture, water, and natural gas with a proppant to form a stimulation fluid. The unfractionated hydrocarbon mixture comprises ethane, propane, butane, isobutane, and pentane plus. The method further comprises increasing a pressure of the stimulation fluid and injecting the stimulation fluid into the subsurface formation.

In one embodiment, a stimulation fluid system comprises an L-Grade storage unit comprising an unfractionated hydrocarbon mixture, water, and natural gas, wherein the unfractionated hydrocarbon mixture comprises ethane, propane, butane, isobutane, and pentane plus; a high pressure pump in fluid communication with the L-Grade storage unit; and at least one of a gelling unit, a foaming agent unit, and a proppant storage unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a stimulation fluid system according to one embodiment.

FIG. 2 is a plan view of a stimulation fluid system according to another embodiment.

FIG. 3 is a plan view of a stimulation fluid system according to another embodiment.

FIG. 4 is a plan view of a stimulation fluid system according to another embodiment.

FIG. 5 is a plan view of a stimulation fluid system according to another embodiment.

FIG. 6 is a plan view of a mobile L-Grade recovery system according to one embodiment.

FIG. 7 is a plan view of a mobile L-Grade recovery system according to one embodiment.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

DETAILED DESCRIPTION

Embodiments of the methods and systems described herein provide a stimulation fluid for treating (such as fracturing) a subsurface formation (such as a hydrocarbon bearing reservoir). The stimulation fluid may be a hydraulic fracturing fluid. The stimulation fluid may comprise naturally occurring, locally available components that are non-damaging to the subsurface formation and cost effective.

L-Grade is an unfractionated hydrocarbon mixture comprising natural gas liquids, condensate (including aromatics), and traces of water, carbon dioxide, and/or hydrogen sulfide. The natural gas liquids in the L-Grade mixture comprise ethane, propane, butane, isobutane, and pentane plus. Pentane plus comprises pentane, isopentane, and/or heavier weight hydrocarbons, for example hydrocarbon compounds containing C5 through C35. Pentane plus may include natural gasoline for example.

Typically, L-Grade is a by-product of de-methanized hydrocarbon streams that are produced from shale wells and transported to a centralized facility. L-Grade typically includes natural gas liquids and condensate with an API gravity ranging between 50 degrees and 75 degrees. In its un-fractionated or natural state (under certain pressures and temperatures, for example within a range of 250-600 psig and at wellhead or ambient temperature) L-Grade has no dedicated market or known use. L-Grade must undergo processing before its true value is proven.

The L-Grade composition can be customized for handling as a liquid under various conditions. Since the ethane content of L-Grade affects the vapor pressure, the ethane content can be adjusted as necessary. According to one example, L-Grade may be processed to have a low ethane content, such as an ethane content within a range of 3-12 percent, to allow the L-Grade to be transported as a liquid in low pressure storage vessels. According to another example, L-Grade may be processed to have a high ethane content, such as an ethane content within a range of 38-60 percent, to allow the L-Grade to be transported as a liquid in high pressure pipelines.

L-Grade differs from liquefied petroleum gas (“LPG”). One difference is that LPG is a fractionated product comprised of primarily propane, or a mixture of fractionated products comprising propane and butane. Another difference is that LPG is a fractioned hydrocarbon mixture, whereas L-Grade is an unfractionated hydrocarbon mixture. Another difference is that LPG is produced in a fractionation facility via a fractionation train, whereas L-Grade can be obtained from an operator's oil & gas production facility. A further difference is that LPG is a pure product with the exact same composition, whereas L-Grade can have a variable composition.

L-Grade can be recovered from a hydrocarbon stream that is collected from the wellhead or production header of one or more unconventional resource wells, typically referred to as shale wells, via flash separation at pressures that are typically below 600 psig. This is accomplished by utilizing flash separation operated at low enough pressure to reject the vast majority of methane from the hydrocarbon stream, but at high enough pressure to retain a significant portion of the ethane plus mixture.

In its unfractionated state, L-Grade is not an NGL purity product and is not a mixture formed by combining one or more NGL purity products. An NGL purity product is defined as an NGL stream having at least 90% of one type of carbon molecule. The five recognized NGL purity products are ethane (C2), propane (C3), normal butane (NC4), isobutane (104) and natural gasoline (C5+). The unfractionated hydrocarbon mixture must be sent to a fractionation facility, where it is cryogenically cooled and passed through a fractionation train that consists of a series of distillation towers, referred to as deethanizers, depropanizers, and debutanizers, to fractionate out NGL purity products from the unfractionated hydrocarbon mixture. Each distillation tower generates an NGL purity product. Liquefied petroleum gas is an NGL purity product comprising only propane, or a mixture of two or more NGL purity products, such as propane and butane. Liquefied petroleum gas is therefore a fractionated hydrocarbon or a fractionated hydrocarbon mixture.

FIG. 1 is a plan view of a stimulation fluid system 100 according to one embodiment. The system 100 includes an L-Grade storage unit 80, a gelling unit 40, and a proppant storage unit 10 fluidly coupled to a blender 30 by piping 20 and 74. L-Grade from the L-Grade storage unit 80 is transferred to a pump 75 through piping 70, to a control valve V1 through piping 72, and to the blender 30 through piping 74. The gelling unit 40 is connected to a dosing pump 50 by piping 60, and the dosing pump 50 is connected to piping 74 by piping 62. A gelling agent is transferred from the gelling unit 40 (through piping 60, the dosing pump 50, and piping 62) into piping 74 and to the blender 30.

The blender 30 receives the L-Grade, the gelling agent, and the proppant (from proppant storage unit 10 via piping 20) mixes them together to form a proppant-laden fracturing fluid. The blender 30 is typically maintained at a pressure of 230 psig to 270 psig, for example about 250 psig. The blender 30 is a mixing vessel, which may be made from any convenient variety of steel, such as carbon steel. The blender 30 may include an abrasion resistant lining, which may include a fluoropolymer such as Teflon. Mixing may be performed using a pumparound. The viscosity of the proppant-laden fracturing fluid may be controlled by adjusting the dosing pump 50. The liquid level in the blender 30 may be controlled by adjusting the flow rates of the L-Grade, the gelling agent, and/or the proppant into the blender 30. Alternately, the flow rates of the L-Grade, the gelling agent, and/or the proppant may be set by recipe control.

The proppant-laden fracturing fluid is transferred from the blender 30 through piping 90 and a control valve V2 into the suction of one or more high-pressure pumps 105, which are typically reciprocating pumps, fluidly coupled to an effluent portal of the blender 30. For the fracturing system 100 shown in FIG. 1, any convenient fracing pump may be used as the high-pressure pumps 105. The high-pressure pumps 105 boost pressure of the proppant-laden fracturing fluid to a wellhead pressure of 250 psig or more, such as 250 psig to 10,000 psig, for example about 10,000 psig, and discharge the pressurized proppant-laden fracturing fluid (also referred to as a stimulation fluid) through piping 150 to a wellhead 190.

FIG. 2 is a plan view of a stimulation fluid system 200 according to another embodiment. The system 200 is similar to the stimulation fluid system 100, with some differences being that the blender 30 has been replaced with a mixer-blender 30 (that can handle high concentrations of proppant), and the gelling unit 40 is replaced with a combination gelling and foaming unit 40 to supply a foaming agent (such as a surfactant) and optionally a gelling agent. The combination gelling and foaming unit 40 may supply a pre-blended mixture (as a liquid and/or a solid) of a foaming agent and a gelling agent into piping 60, and/or may supply a foaming agent and a gelling agent separately but both into piping 60.

L-Grade from the L-Grade storage unit 80 is transferred via pump 75 to piping 74, where it is mixed with a foaming agent (such as a surfactant) and optionally a gelling agent both from the combination gelling and foaming unit 40 and transferred to piping 74 via dosing pump 50. From piping 74, the L-Grade, the foaming agent, optional gelling agent, and proppant (from the proppant storage unit 10) are mixed in the mixer-blender 30 and discharged via piping 90 to the high-pressure pumps 105. The L-Grade, foaming agent, optional gelling agent, and proppant mixture flows through the high-pressure pumps 105, which boosts the pressure of the mixture and discharges the mixture to piping 180 via piping 150.

Liquid nitrogen obtained from the liquid nitrogen source 110, which may be a liquid nitrogen storage unit, is transferred to one or more cryogenic pumps 130 through piping 120. The cryogenic pumps 130 discharge the liquid nitrogen through piping 132 into the vaporizer 135 where the liquid nitrogen is converted into high pressure gaseous nitrogen. The high pressure gaseous nitrogen is discharged via piping 140 to the control valve V3, and from the control valve V3 through piping 145 directly into piping 180, where it mixes with the pressurized L-Grade, foaming agent, optional gelling agent, and proppant mixture to generate foam. The high pressure gaseous nitrogen may be discharged from the vaporizer 135 at a temperature that prevents the formation of hydrates (such as at ambient temperature) when mixed with the pressurized L-Grade, foaming agent, optional gelling agent, and proppant mixture to generate the foam. The foam (also referred to as a stimulation fluid) is then supplied into the wellhead 190 for injection into a subsurface formation.

In the embodiment of FIG. 2, the piping 120, 132 may be resistant to cryogenic temperatures. For example, the piping 120, 132 may be made of cryogenic alloys such as stainless steel, Inconel, and austenitic stainless steel. The low temperature equipment of FIG. 2, such as the piping 120, 132, the liquid nitrogen source 110, the cryogenic pumps 130, and/or the vaporizer 135 may be insulated.

FIG. 3 is a plan view of a stimulation fluid system 300 according to another embodiment. The system 300 is similar to the stimulation fluid system 200, with one difference being that a concentrator 147 has been installed onto piping 150 from the high-pressure pumps 105 to remove excess L-Grade, thus concentrating the remaining pressurized, L-Grade, foaming agent, optional gelling agent, proppant mixture that is discharged into piping 180. Excess L-Grade is removed from the concentrator 147 through piping 106. A choke assembly 165 reduces fluid pressure to enable L-Grade recycling. L-Grade discharged from the choke assembly 165 flows through piping 170 where it is metered by turbine-meter 185 and recycled back into the mixer-blender 30 via piping 74.

Liquid nitrogen obtained from the liquid nitrogen source 110, which may be a liquid nitrogen storage unit, is transferred via piping 120 to one or more cryogenic pumps 130. The cryogenic pumps 130 discharge liquid nitrogen through piping 132 into the vaporizer 135, which converts the liquid nitrogen to high pressure gaseous nitrogen. The high pressure gaseous nitrogen exits the vaporizer 135 via piping 140 into the control valve V3, and from the control valve V3 through piping 145 directly into piping 180, where it mixes with the concentrated L-Grade, foaming agent, optional gelling agent, and proppant mixture in piping 180 to generate foam. The high pressure gaseous nitrogen may be discharged from the vaporizer 135 at a temperature that prevents the formation of hydrates (such as at ambient temperature) when mixed with the concentrated L-Grade, foaming agent, optional gelling agent, and proppant mixture in piping 180 to generate foam. The foam (also referred to as a stimulation fluid) is then supplied into the wellhead 190 for injection into a subsurface formation.

In the embodiment of FIG. 3, the piping 120, 132 may be resistant to cryogenic temperatures. For example, the piping 120, 132 may be made of cryogenic alloys such as stainless steel, Inconel, and austenitic stainless steel. The low temperature equipment of FIG. 3, such as the piping 120, 132, the liquid nitrogen source 110, the cryogenic pumps 130, and the vaporizer 135 may be insulated and may be provided with supplemental cooling as needed.

FIG. 4 is a plan view of a stimulation fluid system 400 according to another embodiment. The system 400 is similar to the stimulation fluid system 200, with one difference being that a pressurized proppant system 177 has been added downstream of the high pressure pumps 105 to replace the proppant storage unit 10 and the mixer-blender 30.

The system 400 includes the L-Grade storage unit 80, the pump 75, the combination gelling and foaming unit 40, the dosing pump 50, one or more high-pressure pumps 105, the liquid nitrogen source 110, one or more cryogenic pumps 130, the vaporizer 135, and the pressurized proppant system 177. L-Grade from the L-Grade storage unit 80 is transferred via pump 75 to piping 74, where it is mixed with a foaming agent (such as a surfactant) and optionally a gelling agent both supplied from the combination gelling and foaming unit 40 and transferred to piping 74 via dosing pump 50. The mixture in piping 74 flows through the high-pressure pumps 105, which boosts the pressure of the mixture and discharges the mixture to piping 180 via piping 150.

Liquid nitrogen obtained from the liquid nitrogen source 110, which may be a liquid nitrogen storage unit, is transferred via piping 120 to one or more cryogenic pumps 130. The cryogenic pumps 130 discharge the liquid nitrogen through piping 132 into the vaporizer 135, which converts the liquid nitrogen to high pressure gaseous nitrogen. The high pressure gaseous nitrogen exits the vaporizer 135 via piping 140 into the control valve V3, and flows from the control valve V3 through piping 145 directly into piping 180 where it mixes with the pressurized L-Grade, foaming agent, and optional gelling agent mixture to generate foam. The high pressure gaseous nitrogen may be discharged from the vaporizer 135 at a temperature that prevents the formation of hydrates (such as at ambient temperature) when mixed with the pressurized L-Grade, foaming agent, and optional gelling agent mixture to generate the foam. Pressurized proppant from the pressurized proppant system 177 is injected via piping 175 into the foam in piping 180. The proppant-laden foam (also referred to as a stimulation fluid) is then supplied into the wellhead 190 for injection into a subsurface formation.

In the embodiment of FIG. 4, the piping 120, 132 may be resistant to cryogenic temperatures. For example, the piping 120, 132 may be made of cryogenic alloys such as stainless steel, Inconel, and austenitic stainless steel. The low temperature equipment of FIG. 4, such as the piping 120, 132, the liquid nitrogen source 110, the cryogenic pumps 130, and the vaporizer 135 may be insulated and may be provided with supplemental cooling as needed.

FIG. 5 is a plan view of a stimulation fluid system 500 according to another embodiment. The system 500 is similar to the stimulation fluid system 200, with one difference being a VorTeq system 178 that has been added to form a closed loop so that the proppant-laden fluid from the mixer-blender 30 does not flow through the high-pressure pumps 105.

The system 500 includes the L-Grade storage unit 80, the pump 75, the combination gelling and foaming unit 40, the dosing pump 50, the proppant storage unit 10, the mixer-blender 30, one or more high-pressure pumps 105, the liquid nitrogen source 110, one or more cryogenic pumps 130, the vaporizer 135, and the VorTeq system 178. L-Grade from the L-Grade storage unit 80 is transferred via pump 75 to piping 74, where it is mixed with a foaming agent (such as a surfactant) and optionally a gelling agent both supplied from the combination gelling and foaming unit 40 and transferred to piping 74 via dosing pump 50. The L-Grade, foaming agent, and optional gelling agent mixture are mixed with proppant from the proppant storage unit 10 in the mixer-blender 30.

The proppant-laden mixture from the mixer-blender 30 flows through the VorTeq system 178 (via piping 90), which pressurizes the proppant-laden mixture using a pressurized fluid (also referred to as a power fluid) supplied from the high-pressure pumps 105 to the VorTeq system 178 via piping 150. The VorTeq system 178 minimizes fluid contact between the power fluid and the proppant-laden mixture, while transferring the hydraulic pressure to boost the pressure of the proppant-laden mixture. The now pressurized proppant-laden mixture discharges to piping 146, and the expended power fluid discharges through piping 151 to a separator 179, which separates out any solid material that may have mixed into the expended power fluid. From the separator 179, the expended power fluid is metered by turbine-meter 185 and cycled back to the high-pressure pumps 105 via piping 170 to be re-pressurized. The re-pressurized power fluid that cycles through the closed loop, including the high-pressure pumps 105, the VorTeq system 178, and the separator 179, may comprise diesel or any other hydrocarbon based fluid, such as an unfractionated hydrocarbon mixture comprising ethane, propane, butane, isobutane, and pentane plus.

Liquid nitrogen obtained from the liquid nitrogen source 110, which may be a liquid nitrogen storage unit, is transferred via piping 120 to one or more cryogenic pumps 130. The cryogenic pumps 130 discharge the liquid nitrogen through piping 132 into the vaporizer 135, which converts the liquid nitrogen to high pressure gaseous nitrogen. The high pressure gaseous nitrogen exits the vaporizer 135 via piping 140 into the control valve V3, and flows from the control valve V3 through piping 145 into piping 180 where it mixes with the pressurized, proppant-laden mixture to generate foam. The high pressure gaseous nitrogen may be discharged from the vaporizer 135 at a temperature that prevents the formation of hydrates (such as at ambient temperature) when mixed with the pressurized, proppant-laden mixture to generate the foam. The proppant-laden foam (also referred to as a stimulation fluid) is then supplied into the wellhead 190 for injection into a subsurface formation.

In the embodiment of FIG. 5, the piping 120, 132 may be resistant to cryogenic temperatures. For example, the piping 120, 132 may be made of cryogenic alloys such as stainless steel, Inconel, and austenitic stainless steel. The low temperature equipment of FIG. 5, such as the piping 120, 132, the liquid nitrogen source 110, the cryogenic pumps 130, and the vaporizer 135 may be insulated and may be provided with supplemental cooling as needed.

In one embodiment, any of the systems 100, 200, 300, 400, 500 may include a VorTeq system (developed by Energy Recovery, Inc.) to protect the high-pressure pumps 105 from damage that may be caused by flowing proppant through the high-pressure pumps 105. Using the VorTeq system, proppant may be routed away from and by-pass the high-pressure pumps 105.

In one embodiment, the high-pressure pumps 105 of any of the systems 100, 200, 300, 400, 500 may be cementing units.

The stimulation fluid provided by any of the systems 100, 200, 300, 400, 500 may be injected into a subsurface formation at a pressure that overcomes the physical strength of the rock of the subsurface formation to fracture the rock formation. In some cases, the pressure needed to fracture the rock formation is about 7,000 psig, but pressures up to 10,000 psig may be used to create fractures at greater depths. As the stimulation fluid is pumped into the rock formation, pressure builds as the rock formation is filled with the stimulation fluid and flow areas become increasingly restricted. When pressure within the rock formation reaches a critical point, sometimes referred to as “breakdown pressure,” fractures begin to nucleate and grow within the rock formation. When the rock formation begins to yield, pressure may drop to a fracture propagation range.

The stimulation fluid provided by any of the systems 100, 200, 300, 400, 500 may comprise a gelling agent. The gelling agent may include phosphate esters, and may additionally include organometallic cross-linking agents.

The stimulation fluid provided by any of the systems 100, 200, 300, 400, 500 may optionally comprise a proppant. The proppant supplied from the proppant storage unit 10 or the pressurized proppant system 177 may be optionally added to any of the stimulation fluids. The proppant may include sand and/or ceramic materials. The proppant may be supplied from a pressurized proppant system.

The stimulation fluid provided by any of the systems 100, 200, 300, 400, 500 may comprise a foaming agent. The foaming agent may comprise one or more surfactants and/or mixtures thereof. The foaming agent may comprise ionic surfactants, nonionic surfactants, anionic surfactants, and/or cationic surfactants. The foaming agent may comprise one or more surfactants having anionic, nonionic, and/or amphoteric structures. The foaming agent may comprise a pure surfactant or a surfactant mixture, may be blended with co-surfactants, and may be aqueous solutions of surfactants and/or co-surfactants, and optionally co-solvents. Co-surfactants may comprise iC90-glycol and/or iC10-glycol. Co-solvents may comprise 1-propanol, iso-propanol, 2-butanol, and/or butyl glycol.

The foaming agent may comprise sulfonic acids, betaine compounds, fluorosurfactants, hydrocarbon solvents, aluminum soaps, phosphate esters, and/or other similar products. Further examples of foaming agents comprise alcoholethersulfates, alcohol sulfate, alcylsulfates, isethionates, sarconisates, acylsarcosinates, olefinsulfonates, alcylethercarboxylates, alcylalcoholamides, aminoxids, alkylbenzolsulfonate, alkylnaphthalene sulfonates, fattyalcohol ethoxylates, oxo-alcohol ethoxylates, alkylethoxylates, alkylphenolethoxylates, fattyamin- and fattyamidethoxylates, alkylpolyglucosides, oxoalcohol ethoxylates, and/or guerbetalcohol alkoxylates. Further examples of foaming agents comprise alkylethersulfonate, EO/PO blockpolymers, and/or betaines such as cocamidopropylbetaine and C8-C10 alkylamidopropylbetaine. Further examples of foaming agents comprise sulfobetaines, alkenylsulfonates, alkylglykols, alcoholalkoxylates, sulfosuccinates, alkyletherphosphates, esterquats, and/or di- and trialcylammoniumderivatives.

The stimulation fluid provided by any of the systems 100, 200, 300, 400, 500 may comprise a foam stabilizer. The foam stabilizer may comprise microparticles or nanoparticles, such as silica or silica derivatives that are known to stabilize foam and emulsions through so-called “pickering”. The foam stabilizer may comprise proteins. The foam stabilizer may comprise additives that increase the viscosity of the stimulation fluid composing the lamella, such as polymeric structures, e.g. polyacrylamide and/or its derivatives.

The stimulation fluid provided by any of the systems 100, 200, 300, 400, 500 may be formed with nitrogen and/or carbon dioxide, and include one or more foaming agents, such as a surfactant, to form foam. The gas content of the stimulation fluid (including the foam for example) may be between about 55% to about 95% by volume.

A mobile high pressure separation and compression system (such as recovery systems 3000 and 4000 shown in FIGS. 6 and 7) can be utilized to recover L-Grade from an individual well or a comingled hydrocarbon stream from several unconventional wells located on a common pad at a wellsite of an oil and gas lease. It is economically attractive to recover and to use the L-Grade from the same oil and gas lease as it eliminates the requirements for the operator to pay mineral royalties and state taxes in most states.

The high pressure mobile separation and compression system is comprised of a three-phase horizontal separator and one or more compressors (such as a natural gas compressor). The three-phase horizontal separator is operated at a specific pressure and temperature to recover a unique composition of L-Grade that can be stored, transported under pressure, and utilized as a stimulation fluid, such as a hydraulic fracturing fluid and/or an enhanced oil recovery fluid. The compressor is utilized to re-pressurize the residual natural gas stream from the three-phase horizontal separator to satisfy offtake wet gas sales pipeline requirements.

FIG. 6 shows a plan schematic of a mobile L-Grade recovery system 3000 according to one embodiment that can be used to create and recover an unfractionated hydrocarbon mixture, such as L-Grade, from a wellhead hydrocarbon stream 310 at a wellsite. The L-Grade recovery system 3000 is transported to the wellsite and connected to the hydrocarbon stream 310 (produced from one or more wells at the wellsite, such as from wellhead 190) via an inlet of a three-phase high pressure horizontal separator 340 with operating pressure and throughput rate controlled by control valve V20. The hydrocarbon stream 310 is separated by the separator 340 into three unique components including L-Grade, water, and natural gas via gravity segregation at a specified pressure.

Pressurized L-Grade exits the separator 340 via transfer line 315 that is controlled by control valve V320 and rate metered by turbine meter M330 to pressurized L-Grade storage vessels 350. Check valve C340 prevents back flow from the L-Grade storage vessels 350. The L-Grade storage vessels 350 are nitrogen blanketed by a nitrogen blanketing system comprising a nitrogen header 360, control valve V370, and liquid nitrogen storage tank 415. Liquid nitrogen from the storage tank 415 via line 390 is vaporized in a nitrogen vaporizer 380 and discharged through the control valve V370 to the nitrogen header 360, which distributes nitrogen into the L-Grade storage vessels 350. The L-Grade can subsequently be used as a stimulation fluid in the form of a foam, a gel, and/or an emulsion, and injected into a hydrocarbon-bearing reservoir (such as through the same well that the hydrocarbon stream 310 was produced, for example wellhead 190) to stimulate and/or fracture the reservoir.

Water from separator 340 is transferred via line 325 to an atmospheric water storage and/or disposal facility on the oil and gas leases for example. The flow rate and pressure of the water from the separator 340 is controlled by valve V130 and metered by turbine meter M120.

Natural gas from the separator 340 is transferred via line 335 through control valve V70 and into a suction scrubber 385. Entrained liquids are removed from the natural gas stream by the suction scrubber 385 and transferred to the atmospheric water storage and/or disposal facility via drain line 319. The suction scrubber 385 can be by-passed by opening control valve V60, closing control valve V70, and allowing the natural gas stream to move through line 395.

A liquid free natural gas stream exits the suction scrubber 385 via line 345, flows through check valve C85, and is suctioned into a suction header 355 for distribution to natural gas compressors 210, 365. The compressors 210, 365 are driven by prime movers 217, 377 via power transfer couplings 215, 375, respectively, to pressurize the natural gas streams. The high pressure natural gas streams exit the compressors 210, 365 into a discharge header 220, and then are cooled by an aftercooler 225, flowed through check valve C290, and metered by an orifice meter M300 before transferring to a wet gas sales line 230 via transfer line 285. The pressurized natural gas stream can also be recycled by opening control valves V250, V260 and at least partially closing control valve V287 to cycle the pressurized natural gas stream back into the compressors 210, 365 via lines 240, 270.

FIG. 7 shows a plan schematic of a mobile L-Grade recovery system 4000 according to one embodiment that can be used to create and recover L-Grade from a wellhead hydrocarbon stream 310 at a wellsite. The L-Grade recovery system 4000 is transported to the wellsite and connected to the hydrocarbon stream 310 (produced from one or more wells at the wellsite, such as from wellhead 190) via an inlet of a three-phase high pressure horizontal separator 340 with operating pressure and throughput rate controlled by control valve V20. The hydrocarbon stream 310 is separated by the separator 340 into three unique components including L-Grade, water, and natural gas via gravity segregation at a specified pressure.

Pressurized L-Grade exits the separator 340 via transfer line 315 that is controlled by control valve V320 and rate metered by turbine meter M330 to pressurized L-Grade storage vessels 350. Check valve C340 prevents back flow from the L-Grade storage vessels 350. The L-Grade storage vessels 350 are nitrogen blanketed by a nitrogen blanketing system comprising a nitrogen header 360, control valve V370, and liquid nitrogen storage tank 415. Liquid nitrogen from the storage tank 415 via line 390 is vaporized in a nitrogen vaporizer 380 and discharged through the control valve V370 to the nitrogen header 360, which distributes nitrogen into the L-Grade storage vessels 350. The L-Grade can subsequently be used as a stimulation fluid in the form of a foam, a gel, and/or an emulsion, and injected into a hydrocarbon-bearing reservoir (such as through the same well that the hydrocarbon stream 10 was produced, for example wellhead 190) to stimulate and/or fracture the reservoir.

Water from separator 340 is transferred via line 325 to an atmospheric water storage and/or disposal facility on the oil and gas leases for example. The flow rate and pressure of the water from the separator 340 is controlled by control valve V130 and metered by turbine meter M120.

Natural gas from the separator 340 is transferred via line 335 into lines 352, 364 that are controlled by control valves V54, V70 and into suction scrubbers 356, 385. Entrained liquids are removed from the natural gas streams by the suction scrubbers 356, 385 and transferred to the atmospheric water storage and/or disposal facility via drain lines 318, 319. The suction scrubbers 356, 385 can be by-passed by opening control valves V62, V64, closing control valves V70, V54, and allowing the natural gas streams to move through lines 392, 395.

A liquid free natural gas stream exits the suction scrubbers 356, 385 via lines 345, 347, flows through check valve C85, C87, and suctioned into a suction header 355 for distribution to compressors 210, 365. The compressors 210, 365 are driven by prime movers 217, 377 via power transfer couplings 215, 375, respectively, to pressurize the natural gas streams. The prime movers 217, 377 may be natural gas engines that are fueled by natural gas delivered from the suction scrubbers 385, 356 via lines 361, 362 that are controlled by valves V58, V62.

The high pressure natural gas streams exit the compressors 210, 365 into a discharge header 220, and then are cooled by an aftercooler 225, flowed through check valve C290, and metered by an orifice meter M300 before transferring to a wet gas sales line 230 via transfer line 285. The pressurized natural gas stream can also be recycled by opening control valves V250, V260 and at least partially closing control valve V287 to cycle the pressurized natural gas stream back into the compressors 210, 365 via lines 240, 270.

In one embodiment, the mobile L-Grade recovery systems 3000, 4000 can be connected to an individual unconventional well or multi-well production facility on an oil and gas lease and located in a designated area classified as Class 1 Division 1 or Division 2 to recover L-Grade and to store the L-Grade for later use in hydraulic fracturing operations.

In one embodiment, the mobile L-Grade recovery systems 3000, 4000 and/or the three-phase horizontal high pressure separator 340 is attached to a portable skid-frame. An example of the separator 340 is a forty inch diameter by ten foot in length carbon steel vessel with a maximum working pressure of 1,440 psig and a liquid and gas capacity of 10,000 barrels of fluid per day and 45 million of cubic feet per day of natural gas, respectively. The inlet of the separator 340 is four inches, the L-Grade outlet of the separator 340 is three inches, the water outlet of the separator 340 is two inches, and the natural gas stream outlet of the separator 340 is three inches, all with ANSI 600 rating. The separator 340 is fitted with a deflector, weir, coalescing plates/filters, a mist extractor, and other safety devices.

In one embodiment, the mobile L-Grade recovery systems 3000, 4000 and/or the compressor(s) 210, 365 driven by the prime mover(s) 217, 377 are attached to a portable skid-frame. An example of the compressors 210, 365 and the prime movers 217, 377 are a reciprocating compressor (or a centrifugal compressor) driven by an electric motor, respectively. A gas turbine powered by the wet gas sales stream can be used to power the prime movers 217, 377. The prime movers 217, 377 can also comprise natural gas fueled engines. The compressors 210, 365 are typically equipped with a suction scrubber, an anti-surge loop, a throttle valve, a shutdown, a speed control, and other safety systems. The typical suction pressure of the compressors 210, 365 would range between 100-230 psig to 250-500 psig, while the typical discharge pressure of the compressors 210, 365 would range between 600 psig to 1,000 psig or 1,500 psig.

In one embodiment, the mobile L-Grade recovery systems 3000, 4000 and/or the suction scrubber(s) 356, 385 are attached to a portable skid-frame. The suction scrubbers 356, 385 are configured to remove entrained liquids and solids from the natural gas stream (that exits from the separator 340) and is typically equipped with replaceable filter elements.

In one embodiment, the mobile L-Grade recovery systems 3000, 4000 and/or the L-Grade storage vessel(s) 350 are attached to a portable skid-frame. An example of an L-Grade storage vessel 350 is a carbon steel bullet shaped shell with a capacity of 30,000-100,000 gallons rated to a maximum working pressure of 250-500 psig.

In one embodiment, the L-Grade storage vessels 350 of the recovery systems 3000, 4000 can be used as the L-Grade storage units 80 of any of the stimulation fluid systems 100, 200, 300, 400, 500. In one embodiment, the L-Grade storage units 80 and/or the L-Grade storage vessels 350 are configured to store pressurized fluid, such as L-Grade, at a pressure of about 250 psig to about 600 psig. In one embodiment, the L-Grade storage units 80 and/or the L-Grade storage vessels 350 have a cleanout access or a manhole through which an operator can access the interior of the units 80 or vessels 350 for cleanout. In one embodiment, the L-Grade storage units 80 and/or the L-Grade storage vessels 350 are internally lined or coated with a corrosion resistant material, such as epoxy, fiberglass, and/or stainless steel.

In one embodiment, the mobile L-Grade recovery systems 3000, 4000 and/or the nitrogen blanketing system is attached to a portable skid-frame. The nitrogen blanketing system can inject liquid nitrogen into the L-Grade storage vessels 350. In one embodiment, the L-Grade in the storage vessels 350 can be injected into a reservoir (through the same or a different well from which the hydrocarbon stream 310 was produced, such as through wellhead 190, as well as into the same or a different reservoir from which the hydrocarbon stream 310 was produced, such as through wellhead 190) to conduct a stimulation operation on the reservoir, such as a fracturing or enhanced oil recovery operation.

In one embodiment, one or more components of the L-Grade recovery systems 3000, 4000 or the entire L-Grade recovery systems 3000, 4000 can be affixed to a portable skid-frame and transported to a wellsite. In one embodiment, different portions of the L-Grade recovery systems 3000, 4000 can be affixed to portable skid-frames, transported to a wellsite, and flanged together at the wellsite to form the entire L-Grade recovery system 3000, 4000. Although described as mobile L-Grade recovery systems 3000, 4000, one or more components of the systems 3000, 4000 (or the entire systems 3000, 4000) may be permanently affixed at a wellsite. In one embodiment, one or more components of the L-Grade recovery systems 3000, 4000 can be remotely monitored during operation to monitor system performance.

While the foregoing is directed to certain embodiments, other and further embodiments may be devised without departing from the basic scope of this disclosure. 

1. A method of treating a subsurface formation, comprising: mixing an unfractionated hydrocarbon mixture, water, and natural gas with a foaming agent to form a stimulation fluid comprising foam, wherein the unfractionated hydrocarbon mixture comprises ethane, propane, butane, isobutane, and pentane plus; increasing a pressure of the stimulation fluid; and injecting the stimulation fluid into the subsurface formation.
 2. The method of claim 1, wherein the foaming agent comprises one or more surfactants.
 3. The method of claim 1, further comprising mixing vaporized nitrogen with the unfractionated hydrocarbon mixture and the foaming agent to form the stimulation fluid.
 4. The method of claim 1, further comprising mixing a foam stabilizer with the unfractionated hydrocarbon mixture and the foaming agent to form the stimulation fluid.
 5. The method of claim 1, further comprising mixing proppant with the unfractionated hydrocarbon mixture and the foaming agent to form the stimulation fluid.
 6. The method of claim 1, further comprising hydraulically fracturing the subsurface formation with the stimulation fluid.
 7. The method of claim 1, further comprising mixing a gelling agent with the unfractionated hydrocarbon mixture and the foaming agent to form the stimulation fluid.
 8. A method of treating a subsurface formation, comprising: mixing an unfractionated hydrocarbon mixture, water, and natural gas with a proppant to form a stimulation fluid, wherein the unfractionated hydrocarbon mixture comprises ethane, propane, butane, isobutane, and pentane plus; increasing a pressure of the stimulation fluid; and injecting the stimulation fluid into the subsurface formation.
 9. The method of claim 8, further comprising mixing a foaming agent with the unfractionated hydrocarbon mixture and the proppant to form the stimulation fluid.
 10. The method of claim 8, further comprising mixing a gelling agent with the unfractionated hydrocarbon mixture and the proppant to form the stimulation fluid.
 11. The method of claim 8, further comprising mixing vaporized nitrogen with the unfractionated hydrocarbon mixture and the proppant to form the stimulation fluid.
 12. A stimulation fluid system, comprising: an L-Grade storage unit comprising an unfractionated hydrocarbon mixture, water, and natural gas, wherein the unfractionated hydrocarbon mixture comprises ethane, propane, butane, isobutane, and pentane plus; a high pressure pump in fluid communication with the L-Grade storage unit; and at least one of a gelling unit, a foaming agent unit, and a proppant storage unit.
 13. The system of claim 12, further comprising a liquid nitrogen source in fluid communication with a vaporizer that is in fluid communication with the high pressure pump.
 14. The system of claim 12, further comprising a mixer-blender in fluid communication with the L-Grade storage unit and at least one of the gelling unit, the foaming agent unit, and the proppant storage unit.
 15. The system of claim 12, further comprising a pressurized proppant supply located downstream of the high pressure pump. 